Allergen-specific immunotherapy induces Th1 shift in dogs with atopic dermatitis

Allergen-specific immunotherapy has been applied to canine atopic dermatitis. Despite the accumulated clinical evidence of its effect for atopic dogs, the basic immunologic mechanisms were not fully understood. In this study, the cytokine profile ex vivo in canine atopic dermatitis before and after allergen-specific immunotherapy was characterized using competitive reverse transcription–polymerase chain reaction (RT–PCR). Blood samples were collected from 10 dogs with atopic dermatitis and peripheral blood mononuclear cells were stimulated with house dust mite antigen. The levels of IFN-γ and IL-4 mRNA were lower in atopic dogs compared with non-atopic controls. The ratio of IFN-γ/IL-4 was low in atopic dogs indicating a cytokine profile polarized to Th2. The level of IFN-γ after immunotherapy was significantly higher than that before (P < 0.05) whereas that of IL-4 mRNA was not changed. Consequently, the ratio of IFN-γ/IL-4 after immunotherapy was significantly higher than that before immunotherapy (P < 0.05). These results indicate a Th2 cytokine bias is the dominant state in atopic dogs and allergen-specific immunotherapy causes a shift to wards a Th1 bias by enhancing IFN-γ expression.